Removes arcanist and Phabricator information. (#82115)

Removes old arcanist configuration files and documentation of
Phabricator. This only removes the data that seems save to remove.

Author: mordante

.arcconfig

@@ -89,10 +89,9 @@ in order to update the last commit with all pending changes.
   ``clang/tools/clang-format/git-clang-format``.
 
 The LLVM project has migrated to GitHub Pull Requests as its review process.
-We still have an active :ref:`Phabricator <phabricator-reviews>`
-instance for the duration of the migration. If you want to contribute to LLVM
-now, please use GitHub. For more information about the workflow of using GitHub
-Pull Requests see our :ref:`GitHub <github-reviews>` documentation.
+For more information about the workflow of using GitHub Pull Requests see our
+:ref:`GitHub <github-reviews>` documentation. We still have an read-only
+`LLVM's Phabricator <https://reviews.llvm.org>`_ instance.
 
 To make sure the right people see your patch, please select suitable reviewers
 and add them to your patch when requesting a review. Suitable reviewers are the
@@ -185,5 +184,5 @@ of LLVM's high-level design, as well as its internals:
 .. _clang-format-diff.py: https://reviews.llvm.org/source/llvm-github/browse/main/clang/tools/clang-format/clang-format-diff.py
 .. _git-clang-format: https://reviews.llvm.org/source/llvm-github/browse/main/clang/tools/clang-format/git-clang-format
 .. _LLVM's GitHub: https://github.com/llvm/llvm-project
-.. _LLVM's Phabricator (deprecated): https://reviews.llvm.org/
+.. _LLVM's Phabricator (read-only): https://reviews.llvm.org/
 .. _LLVM's Open Projects page: https://llvm.org/OpenProjects.html#what

.arclint

@@ -129,8 +129,8 @@ awareness of. For such changes, the following should be done:
 
 .. warning::
 
-  Phabricator is deprecated and will be switched to read-only mode in October
-  2023, for new code contributions use :ref:`GitHub Pull Requests <github-reviews>`.
+  Phabricator is deprecated is available in read-only mode,
+  for new code contributions use :ref:`GitHub Pull Requests <github-reviews>`.
   This section contains old information that needs to be updated.
 
 * When performing the code review for the change, please add any applicable